1. Technical Field of the Invention
The present invention relates to a liquid ejection head which ejects liquid supplied from a liquid cartridge or the like, as liquid droplets, and more particularly to a liquid ejection head in which a flow path forming substrate constituting a flow path unit can be prevented from being broken, and a method of producing same.
2. Description of the Related Art
An ink-jet recording apparatus which is a typical example of a liquid ejection apparatus has a configuration in which an ink-jet recording head (liquid ejection head) having: pressure generating means for pressurizing a pressure generating chamber; and a nozzle opening from which a pressurized ink is ejected as an ink droplet is mounted on a carriage.
In a multi-nozzle ink-jet recording head in which plural nozzle openings are arranged in one substrate, a nozzle plate in which plural nozzle openings are opened, a flow path forming substrate in which a space serving as pressure generating chambers and ink supply flow paths is formed, and a vibration plate which seals another face are stacked and joined together. A pressure is generated in the pressure generating chambers by deformation stress of the vibration plate caused by a piezoelectric vibrator, thereby ejecting ink droplets from the nozzle openings (for example, JP-A-2000-62164).
FIGS. 8 and 9 show a flow path forming substrate 50 in a related art recording head. The flow path forming substrate 50 comprises pressure generating chambers 51 which are disposed in a row, and ink reserving chambers 53 which are disposed along the row of the pressure generating chambers 51, and which reserves an ink to be supplied to the pressure generating chambers 51 through ink supply paths 52. In this example, two rows of pressure generating chambers 51 are formed, and a total of two ink reserving chambers 53 are disposed so as to respectively correspond to the rows of the pressure generating chambers 51.
In the flow path forming substrate 50, a space corresponding to the pressure generating chambers 51, the ink supply paths 52, and the ink reserving chambers 53 is formed by anisotropically etching a monocrystal silicon substrate, and each of the ink reserving chambers 53 is formed as a space which vertically penetrates from one face of the substrate to the other face.
In the recording head, an end portion (the portion K in FIG. 8, and the portion L in FIG. 9) of each of the ink reserving chambers 53 in the row direction of the pressure generating chambers 51 is narrowed so that the width of the ink reserving chamber 53 is tapered, thereby improving the property of discharging air bubbles staying in the end portion of the ink reserving chamber 53 (see JP-A-2000-62164).
As shown in FIG. 10, in the end portion (the portion K in FIG. 8, and the portion L in FIG. 9) of each of the ink reserving chambers 53 in the row direction of the pressure generating chambers 51 in the flow path forming substrate 50, a projection 54 having a triangular section shape is formed in the vicinity of a middle area in the thickness direction of the width-tapered portion of the ink reserving chamber 53. The projection 54 is formed in the process of forming the ink reserving chamber 53 by anisotropic etching of the monocrystal silicon substrate.
FIG. 11 is a view showing steps of producing the conventional flow path forming substrate 50. First, a monocrystal silicon substrate 55 which is cut out so that a plane of crystal plane orientation of (110) is the surface is prepared. A pattern of a silicon oxide film 56 is formed on the both faces of the silicon substrate 55 by photo-etching using a resin resist (FIG. 11A). In the illustrated state, as a result of the patterning, an etching region 57 where the silicon oxide film 56 does not exist is formed in portions which will be formed as the ink reserving chambers 53, on the upper and lower faces of the silicon substrate 55.
Then, anisotropic etching is performed with using an etching solution such as an aqueous solution of potassium hydroxide, to etch the surfaces of the etching regions 57 on the both or upper and lower faces of the monocrystal silicon substrate 55. At this time, the etching advances while a (111) plane which is inclined by about 35 deg. with respect to the (110) plane appears (FIG. 11B). In a state where the etching portions on the upper and lower faces communicate with each other to achieve penetration, the (111) plane appearing from the upper faces meets that appearing from the lower faces, and a ridge edge is formed by the two (111) planes (FIG. 11C).
When the upper and lower (111) planes meet together to form the ridge, the etching advances while a (111) plane perpendicular to the (110) plane appears in end portions of the silicon oxide film 56, i.e., boundary portions between the region masked by the silicon oxide film 56 and the etching regions where the silicon oxide film 56 does not exist (FIG. 11D). As a result of such etching behavior, the projections 54 having a triangular section shape are finally formed on end portions in the row direction of the pressure generating chambers 51 of the ink reserving chamber 53.
When such projections 54 are formed in the flow path forming substrate 50, however, stress concentration easily occurs in a portion where the ridge portion of each of the projections 54 is in contact with the wall face. When the projection 54 exists in the tapered end portion of the ink reserving chamber 53, particularly, stress is further concentrated in the portion. Consequently, there is a problem in that, when stress concentration occurs in the portion, the flow path forming substrate 50 cracks in handling in production steps and becomes a defective product, thereby lowering the production yield. When the projection 54 exists on the inner wall face of the ink reserving chamber 53, the ink flow is blocked by the projection 54. Consequently, there is another problem in that the air bubble discharging property in the case where air bubbles staying in the ink reserving chamber 53 are forcibly sucked to be discharged through the nozzle openings is impaired. Particularly, the vicinity of the nozzle row end of the ink reserving chamber 53 is a place where the air bubble discharging property easily becomes problematic. The existence of the projection 54 in such a place imposes a large adverse affect on the air bubble discharging property.